IC cards have been increasingly used in various aspects from users' daily lives to business activities. Actually, they are used, for example, as various cards (e.g., cash cards, credit cards, prepaid cards and ETC cards (electronic toll collection system)); in transportation facilities (e.g., railways and buses); as affiliate cards for digital broadcasting, 3rd generation (3G) mobile phones; in library service counters; and as student ID cards, employee ID cards, basic resident register cards. Meanwhile, the amount of IC cards disposed of has been being increasing in accordance with diversification of the current economic and social activities. In view of this, there is a keen need to create a recycling society, where material consumption is reduced and less environmental load is given, by reconsidering the current economic societies and lifestyles involving mass production, mass consumption and mass disposal to promote effective utilization and recycling of materials.
As one promising measure, electronic information recording element-embedded thermoreversible recording media (RFID tag) (hereinafter the electronic information recording element may be referred to as an “IC chip module” or “IC chip”), can be used for reducing the amount of products disposed of. This is because they can rewrite information stored in the IC chip and show information as a visible image on their surface.
Such IC chip module-embedded thermoreversible recording media have been used in the manufacturing industry as instruction sheets such as operation sheets, parts management sheets and process management sheets. Actually, there is repeatedly performed a cycle including winding an instruction sheet around a rod-like part or inserting it into a card case, and rewriting the content of the instruction sheet.
When an image is formed on or erased from it, a heating device (e.g., thermal head, erase bar, erase roller and erase plate) of the printer is pressed against the instruction sheet. Thus, rewriting of a print image on the instruction sheet (i.e., thermoreversible recording medium) must be performed so as not to break the IC chip module and not to avoid overflow of an adhesive from an adhesion portion between the IC chip module and the thermoreversible recording medium. Furthermore, desirably, the instruction sheet is flexible and shows a high-quality image.
High print quality of images is maintained by improving close-contact properties of the surface of a reversible thermosensitive recording layer with a printer head. In order to improve the close-contact properties, a thermoreversible recording medium must be thin and uniform in total thickness.
However, the thickness of an inlet portion and the thickness of an IC chip portion of an electronic information recording element cause a bottleneck to make the total thickness of the thermoreversible recording medium to be thin and uniform. By absorbing these thicknesses into an adhesive or a base, the total thickness of the thermoreversible recording medium can be made thin while the surface of the reversible thermosensitive recording layer being kept smooth.
Moreover, there is a problem that air bubbles 610 tend to be included in corners of the surrounding area of an inlet 600, when the inlet is mounted by laminating sheets, as illustrated in FIG. 1. The inclusion of the air bubbles at the corners of the surrounding of the inlet 600 may cause surface unevenness of a thermoreversible recording medium, leading to recording and erasure failures as the thermoreversible recording medium is printed by a printer.
When an inlet sheet and an adhesive sheet are laminated by a pair of rubber nip rollers, for example, the inlet is nipped with the surfaces of the two nip rollers. As the sheets enter into the space between the nip rollers with the surrounding of the inlet forming a triangle space due to the height of the inlet, and the air included therein, air bubbles are included in a final product. As a diameter of the roller increases, more likely air bubbles are included therein.
In order to solve the aforementioned problems, for example, proposed is a method for producing an IC card containing: supplying an adhesive from multiple nozzles to apply the adhesive in the form of a plurality of lines on at least part of a surface of an inlet film, a surface of a surface film, or both; laminating the inlet film and the surface film; and compressing the laminate to roll out the adhesive applied in the form of lines, to thereby bond the inlet film with the surface film (see PTL 1).
In the proposed method, after applying the adhesive in the form of the multiple lines, the laminate is pressed by a press roller to give a desirable thickness of the adhesive over the entire width. In this method, however, the adhesive liquid is dropped on the inlet film from the top while the inlet film is transported, and the sheets are bonded just after air bubbles are included. Therefore, there is a possibility that air bubbles are enclosed at the points where the rolled out adhesive meets with the other.
Accordingly, it has been desired to provide a method for continuously producing with high efficiency a thermoreversible recording medium being thin and uniform in total thickness which method enables lamination without inclusion of air bubbles and prevention of recording failure and print failure caused by surface unevenness.